. A text book of physics, for the use of students of science and engineering . drawn through them. Two other lines CD and EF are then drawn, parallel to AB, so that the trace CE is made by one fork in the same time that the trace DF is made by the other. On counting the numbers of vibrations in CE and DF the ratio of the frequencies of the forks can be found. In 26-5the given case it is -p—-=1-325, 20 The aluminium style should be bent to the shape shown at S (Fig. 609). 666 SOUND CHAP. As the plate falls, the style can then bend slightly, owing to the plate press-ing against it, hut the level
. A text book of physics, for the use of students of science and engineering . drawn through them. Two other lines CD and EF are then drawn, parallel to AB, so that the trace CE is made by one fork in the same time that the trace DF is made by the other. On counting the numbers of vibrations in CE and DF the ratio of the frequencies of the forks can be found. In 26-5the given case it is -p—-=1-325, 20 The aluminium style should be bent to the shape shown at S (Fig. 609). 666 SOUND CHAP. As the plate falls, the style can then bend slightly, owing to the plate press-ing against it, hut the level of the pcint is not altered by this bending. Expt. 152.—To find the absolute frequency of a fork by tbe dropping the determination of the absolute frequency of a fork by the droppingplate method, the plate must fall freely. The guides are therefore dis-pensed with and the plate is suspended by the thread A (Fig. 611), andcan be released by burning the thread at A. The style must be made asin the last experiment and the bowing of the fork performed as Fig. 611.—Dropping plate for measurementof absolute frequency. FlO. 612.—Trace bysingle fork. An example of the kind of trace produced is given in Fig. 612. Thestarting point A must be clearly marked. By means of a cathetometeror travelling microscope, the distances sl and s2 to any clearly markedwaves at B and C can be found. Then, the time t1 required for the plate to fall through the distance stfrom the start is given by s^ = \gt^, where g is the acceleration of gravity (p. 33). Therefore ^ = a/—• 9 IW Again, the time required by the, plate to fall from A to C is t-> = /\--i Hence the time occupied in falling from B to C is calculated from 9 >^Hf LII THE CHRONOGRAPH G67 In this time the number of vibrations n made by the fork can be counted, then n Frequency of fork = 7——•t2 — li In the given case n--21 and sx = l-54 cm., s2=9-27 cm.; .. taking g as 981 cm. per sec. per sec. t2 - ti
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